The ultra thin copper foil with a carrier is used in the electronics industry as a high-density and fine line printed circuit board assembly, what to be emphasized today are supposed to light, thin, short and small, precision requirements for the circuit lines trend toward accuracy, and the demand of copper foil thinning processing is growing. The current ultra thin copper foil with a carrier generally is composed of an 18˜35 μm thickness carrier (copper or aluminum foil), whereon an ultra thin copper foil of 1˜6 μm thickness is electroplated.
With the high density requirement of various electronic components, the circuit board composites and circuit patterns thereof are also required to be high density, for example, as for printed circuit boards used in packaging, the track width and track spacing between the circuit lines are needed to be about 30 μm for the high density micro-circuits, the use of a thick electrodeposited copper foil will increase the etching time, the result will be that the vertical degree of the circuit pattern sidewall is destructed; a short circuit or a break circuit will not be formed in the wide line spacing circuit, but may happen in the narrow line spacing circuit.
The release layer between the carrier foil and the ultra thin copper foil is generally organic-based nitrogen containing organic compounds or inorganic-based chromium metal or chromate binary alloy inorganic film. The disadvantages of using the organic release film layer are not only the disposal treatments of the plating bath and wastewater which increase treatment costs and time, but also bubbles arise in the high temperature circuit board manufacturing process which affect the circuit board manufacturing quality and induce electricity test instability. On the other hand, the release film layer is composed of an inorganic based binary alloy, the ratio of its film thickness is the important factor to control the bonding strength of the ultra thin copper foil with the carrier foil, if the ratio control is poor, it is prone to peel incompletely or easy to peel so that the oxidation discoloration after lamination occurs.
The ultra thin copper foil used for a micro-thin circuit pattern is formed by electrolytic deposition directly on the release layer of the carrier foil, the best thickness of the ultra thin copper is below 5 μm. As the surface morphology of the carrier foil directly affects the release layer and the ultra thin copper foil, when the carrier surface roughness is higher, the subsequent electroplated ultra thin copper foil is also easy to have a high roughness, thereby the etching is affected. In addition, the uneven surface morphology of the carrier foil will also affect the thickness uniformity of the ultra thin copper foil for a time. At the same time when the carrier foil with pinholes, the ultra thin copper foil will also have pinholes. The carrier foil is the basis for the release layer and the ultra thin copper foil, therefore the choice of the carrier copper foil is very important. A traditional HTE (High Temperature Elongation) copper foil, or a rolled copper foil is used mainly as a carrier in former inventions, but the HTE copper foil is likely to have poor surface uniformity and pinhole problems. On the other hand, due to width and cost problems, the rolled copper foil will limit the application of products.
In addition, the laminating surface (mat) of the ultra thin foil is laminated with epoxy resin substrate, the laminating surface of the ultra thin foil undergoes a roughening treatment, anti-rust treatment and silane coating treatment and so on, all of them are closely related to adhesion to the substrate, which significantly affects the product qualities.